This invention relates generally to downhole tools and methods for manufacturing such items. More particularly, this invention relates to infiltrated matrix drilling products including, but not limited to, fixed cutter bits, polycrystalline diamond compact (“PDC”) drill bits, natural diamond drill bits, thermally stable polycrystalline (“TSP”) drill bits, bi-center bits, core bits, and matrix bodied reamers and stabilizers, and the methods of manufacturing such items.
Full hole tungsten carbide matrix drill bits for oilfield applications have been manufactured and used in drilling since at least as early as the 1940's. FIG. 1 shows a cross-sectional view of a downhole tool casting assembly 100 in accordance with the prior art. The downhole tool casting assembly 100 consists of a thick-walled mold 110, a stalk 120, one or more nozzle displacements 122, a blank 124, a funnel 140, and a binder pot 150. The downhole tool casting assembly 100 is used to fabricate a casting (not shown) of a downhole tool.
According to a typical downhole tool casting assembly 100, as shown in FIG. 1, and a method for using the downhole tool casting assembly 100, the thick-walled mold 110 is fabricated with a precisely machined interior surface 112, and forms a mold volume 114 located within the interior of the thick-walled mold 110. The thick-walled mold 110 is made from sand, hard carbon graphite, ceramic, or other known suitable materials. The precisely machined interior surface 112 has a shape that is a negative of what will become the facial features of the eventual bit face. The precisely machined interior surface 112 is milled and dressed to form the proper contours of the finished bit. Various types of cutters (not shown), known to persons having ordinary skill in the art, can be placed along the locations of the cutting edges of the bit and can also be optionally placed along the gage area of the bit. These cutters can be placed during the bit fabrication process or after the bit has been fabricated via brazing or other methods known to persons having ordinary skill in the art.
Once the thick-walled mold 110 is fabricated, displacements are placed at least partially within the mold volume 114 of the thick-walled mold 110. The displacements are typically fabricated from clay, sand, graphite, ceramic, or other known suitable materials. These displacements consist of the center stalk 120 and the at least one nozzle displacement 122. The center stalk 120 is positioned substantially within the center of the thick-walled mold 110 and suspended a desired distance from the bottom of the mold's interior surface 112. The nozzle displacements 122 are positioned within the thick-walled mold 110 and extend from the center stalk 120 to the bottom of the mold's interior surface 112. The center stalk 120 and the nozzle displacements 122 are later removed from the eventual drill bit casting so that drilling fluid (not shown) can flow though the center of the finished bit during the drill bit's operation.
The blank 124 is a cylindrical steel casting mandrel that is centrally suspended at least partially within the thick-walled mold 110 and around the center stalk 120. The blank 124 is positioned a predetermined distance down in the thick-walled mold 110. According to the prior art, the distance between the outer surface of the blank 124 and the interior surface 112 of the thick-walled mold 110 is typically 12 millimeters (“mm”) or more so that potential cracking of the thick-walled mold 110 is reduced during the casting process.
Once the displacements 120, 122 and the blank 124 have been positioned within the thick-walled mold 110, tungsten carbide powder 130 is loaded into the thick-walled mold 110 so that it fills a portion of the mold volume 114 that is around the lower portion of the blank 124, between the inner surfaces of the blank 124 and the outer surfaces of the center stalk 120, and between the nozzle displacements 122. Shoulder powder 134 is loaded on top of the tungsten carbide powder 130 in an area located at both the area outside of the blank 124 and the area between the blank 124 and the center stalk 120. The shoulder powder 134 is made of tungsten powder or other known suitable material. This shoulder powder 134 acts to blend the casting to the steel blank 124 and is machinable. Once the tungsten carbide powder 130 and the shoulder powder 134 are loaded into the thick-walled mold 110, the thick-walled mold 110 is typically vibrated to improve the compaction of the tungsten carbide powder 130 and the shoulder powder 134. Although the thick-walled mold 110 is vibrated after the tungsten carbide powder 130 and the shoulder powder 134 are loaded into the thick-walled mold 110, the vibration of the thick-walled mold 110 can be done as an intermediate step before, during, and/or after the shoulder powder 134 is loaded on top of the tungsten carbide powder 130.
The funnel 140 is a graphite cylinder that forms a funnel volume 144 therein. The funnel 140 is coupled to the top portion of the thick-walled mold 110. A recess 142 is formed at the interior edge of the funnel 140, which facilitates the funnel 140 coupling to the upper portion of the thick-walled mold 110. Typically, the inside diameter of the thick-walled mold 110 is similar to the inside diameter of the funnel 140 once the funnel 140 and the thick-walled mold 110 are coupled together.
The binder pot 150 is a cylinder having a base 156 with an opening 158 located at the base 156, which extends through the base 156. The binder pot 150 also forms a binder pot volume 154 therein for holding a binder material 160. The binder pot 150 is coupled to the top portion of the funnel 140 via a recess 152 that is formed at the exterior edge of the binder pot 150. This recess 152 facilitates the binder pot 150 coupling to the upper portion of the funnel 140. Once the downhole tool casting assembly 100 has been assembled, a predetermined amount of binder material 160 is loaded into the binder pot volume 154. The typical binder material 160 is a copper alloy or other suitable known material. Although one example has been provided for setting up the downhole tool casting assembly 100, other examples can be used to form the downhole tool casting assembly 100.
The downhole tool casting assembly 100 is placed within a furnace (not shown) or other heating structure. The binder material 160 melts and flows into the tungsten carbide powder 130 through the opening 158 of the binder pot 150. In the furnace, the molten binder material 160 infiltrates the tungsten carbide powder 130 to fill the interparticle space formed between adjacent particles of tungsten carbide powder 130. During this process, a substantial amount of binder material 160 is used so that it fills at least a substantial portion of the funnel volume 144. This excess binder material 160 in the funnel volume 144 supplies a downward force on the tungsten carbide powder 130 and the shoulder powder 134. Once the binder material 160 completely infiltrates the tungsten carbide powder 130, the downhole tool casting assembly 100 is pulled from the furnace and is controllably cooled. Upon cooling, the binder material 160 solidifies and cements the particles of tungsten carbide powder 130 together into a coherent integral mass 310 (FIG. 3). The binder material 160 also bonds this coherent integral mass 310 (FIG. 3) to the steel blank 124 thereby forming a bonding zone 190, which is formed along at least a chamfered zone area 198 of the steel blank 124 and a central zone area 199 of the steel blank 124. The coherent integral mass 310 (FIG. 3) and the blank 124 collectively form the matrix body bit 200 (FIG. 2), a portion of which is shown in FIGS. 2 and 3. Once cooled, the thick-walled mold 110 is broken away from the casting. The casting then undergoes finishing steps which are known to persons having ordinary skill in the art, including the addition of a threaded connection (not shown) coupled to the top portion of the blank 124. Although the matrix body bit 200 (FIG. 2) has been described to be formed using the process and equipment described above, the process and/or the equipment can be varied to still form the matrix body bit 200 (FIG. 2).
FIG. 2 shows a magnified cross-sectional view of the bonding zone 190 located at the chamfered zone area 198 (FIG. 1) within the matrix body bit 200 in accordance with the prior art. FIG. 3 shows a magnified cross-sectional view of the bonding zone 190 located at the central zone area 199 (FIG. 1) within the matrix body bit 200 in accordance with the prior art. Referring to FIGS. 2 and 3, the coherent integral mass 310 is bonded to the steel blank 124 via the bonding zone 190 that is formed along the surface of the steel blank 124 and which extends inwardly into the interior portion of the steel blank 124. A portion of the binder material 160 diffuses into the steel blank 124 and reacts with the steel blank 124 to form this bonding zone 190. The bonding zone 190 includes intermetallic compounds 290. These intermetallic compounds 290 have an average hardness level of about 250 HV, which corresponds to about twice the hardness of the binder and steel matrix. According to FIG. 2, the bonding zone 190 is formed having a thickness 215 ranging from about sixty-five micrometers (μm) to about eighty μm in the chamfered zone area 198 (FIG. 1). According to FIG. 3, the bonding zone 190 is formed having a thickness 315 ranging from about ten μm to about twenty μm in the central zone area 199 (FIG. 1). The thicknesses 215, 315 and/or volumes of the bonding zone 190 are dependent upon the exposure time and the exposure temperature. Exposure temperature is related to the type of binder material 160 that is used to cement the tungsten carbide particles to one another. Manufacturers typically use the same binder material 160 over long periods of time, such as ten year or more, because of the knowledge gained with respect to the binder material 160 used. Thus, the exposure temperature is substantially the same from one casting to another. Exposure time is not always the same, but instead, is related to the bit diameter that is to be manufactured. When the bit diameter to be manufactured is relatively large, there is a larger volume of tungsten carbide particles that cemented to one another. Hence, the exposure time also is relatively longer, thereby providing more time for cementing the larger volume of tungsten carbide particles. Thus, since the exposure temperature is the same from one casting to another, and the exposure time is the same for casting similar bit diameters, it follows that the thicknesses 215, 315 of intermetallic compounds 290 formed within the bit is consistent from one casting to another for a same bit diameter.
Initially, natural diamond bits were used in oilfield applications. These natural diamond bits performed by grinding the rock within the wellbore, and not by shearing the rock. Thus, these natural diamond bits experienced little to no torque, and hence very little stress was experienced at the bonding zone 190 of the natural diamond bits. With the advent of PDC drill bits, the bits sheared the rock within the wellbore and began experiencing more torque. However, these initial PDC drill bits were fabricated relatively small, about six inch diameters to about 12¼ inch diameters, and the prior art fabrication method described above continued to perform well. Later, PDC drill bits were fabricated having larger diameters and failures began occurring along the bonding zone 190. Specifically, decohesion began occurring between the blank 124 and the coherent integral mass 310, or matrix, at the bonding zone 190. These intermetallic compounds 290 are a source for causing mechanical stresses to occur along the bonding zone 190 during drilling applications because there is a contraction of volume occurring when the intermetallic compounds 290 are formed. Now that cutter technology has improved, the demand placed upon the bits have also increased. Bits are being drilled for more hours. Bits also are being used with much more energy, which includes energy produced from increasing the weight on bit and/or from increasing the rotational speed of the bit. This increased demand on the bits is causing the decohesion failure to become a recurring problem in the industry. As the thickness or volume of the intermetallic compounds 290 increases, the risk of decohesion also increases.